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Methionine and sulfer metabolism
EVMS biochem lecture 41
33
Biochemistry
Graduate
04/25/2011

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Term
Methionine:
Definition
donates an “activated” methyl group for syntheses
provides sulfur for synthesis of cysteine
provides the activated amine for polyamine synthesis
Term
Cysteine:
Definition
constituent of glutathione (-Glu-Cys-Gly)
precursor of taurine
source of sulfate (SO42- ) for PAPS (activated sulfate
Term
PAPS
Definition
3’-phosphoadenosine 5’phosphosulfate
Synthesis of iron-sulfur proteins
Sulfation of oligosaccharides such as heparin sulfate
Sulfation of hormones, including steroids, T3, T4
Term
Methionine adenosyltransferase
Definition
catalyzes SAM production from Methionine, needs ATP, releases PPi and Pi
Term
S-adenosylhomocysteine
Definition
formed when a methyl group is donated to SAM
Term
homocysteine
Definition
released from S-adenosylhomocysteine and can be remethylated to methionine, an analog of cystein with an extra CH2 in its carbon backbone
Term
epinephrine
Definition
methylated product of NE
Term
creatine
Definition
methylated product of guanidinoacetate
Term
phosphatidylcholine
Definition
the methylated product of phosphatidylethanolamine
Term
melatonin
Definition
methylated product of acetylserotonin
Term
sarcosine (N methylglycine)
Definition
methylated product of glycine
Term
photphatidylcholine
Definition
synthesis of this requires three successive methylation reactions
Term
creatine phosphate
Definition
provides immediate energy in muscle, ATP can then resynthesize
Term
creatinine
Definition
24 hour urine concentration is a function of muscle mass, elevated plasma levels indicates impaired renal function
Term
arginine, glycine, and SAM
Definition
precursors of creatine
Term
GAMT, AGAT, and SLC6A8 deficiency
Definition
the 3 cerebral creatine deficiency syndromes
Term
GMAT deficiency
Definition
Mental retardation and seizures
Approximately 80% of individuals have a behavior disorder that can include autistic behaviors and self-mutilation
Onset is between ages three months and three years.
Term
homocystine
Definition
oxidized dimer of homocysteine
Term
tHcy
Definition
used to designate a mixture of homocysteine and homocystine
Term
methyl FH4
Definition
methylation of homocysteine to form methionine requires
Term
betaine
Definition
can also donate a ch3 to B12, liver and kidney, oxidation product of choline
Term
cystathionine
Definition
intermediate in cystein synthesis pathway, fromed by condensation of homocysteine and serine, cleaved by hydrolysis
Term
GSH
Definition
tripeptide synthesized by sequential addition of cysteine and then glycine to glutamate, protects from oxidation, detoxify h2o2, FA peroxides, and xenobiotis, synthesis of leukotriene C4 and contributs to amino acid absorption
Term
glutathione peroxidase
Definition
a selenium containing enzyme which removes h2o2 and minimized oxidative damage
Term
glutathione reductase
Definition
reduced GSH is regenerated from oxidized GSSG by
Term
LTC4
Definition
a peptidyl leudotriene which contains glutathione, formed via the lipoxygenase pathway from arachidonic acid, potent stimulant of bronchoconstriction
Term
y-glutamyl cycle
Definition
cycle that occurs in kidney and intestine, transpeptidase attaches extracellular AA to GSH to facilitate AA transfer into the cell
Term
taurine
Definition
an amino sulfonic acid, sulfate instead of carboxyl, not used for protein synthesis
Term
oxidation, decarboxylation, oxidation
Definition
reactions to produce taurine from cysteine
Term
taurine
Definition
although adults form both glycine and taurine conjugates for bile salts, neonates only use
Term
taurine
Definition
abundant intracellularly in retina and leukocytes, brain and retinal development, osmoregulation, modulation of Ca processes, and membrane stabilization
May regulate the expression of genes required for glucose-stimulated insulin secretion
May enhance peripheral insulin sensitivity
May decrease atherosclerosis
Term
oxidative stress or iron overload
Definition
taurine may protect against
Term
premature infants
Definition
have a lower store or taurine, inefficient reabsorption of taurine, low activity of cystathionase
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